Angular's HTML5 mode overrides the default routing, so routes that appear valid only exist when you visit them after initializing the app.
This means if I were to set up an angular route called /about and tried going to localhost, then clicking on a link to /about, everything would work. But if I tried refreshing once I was on the localhost/about page, or going directly to localhost/about I would get a 404.
To fix this I will set all unspecified server routes to go to index.html. This will also require a rendering engine such as EJS to render the html page on request.